AU2008220931A1

AU2008220931A1 - Method and arrangement for separating magnetic particles from a substance

Info

Publication number: AU2008220931A1
Application number: AU2008220931A
Authority: AU
Inventors: Manfred Ruhrig
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2007-02-28
Filing date: 2008-02-05
Publication date: 2008-09-04
Anticipated expiration: 2028-02-05
Also published as: DE102007010130A1; AR065489A1; AU2008220931B2; WO2008104445A1; BRPI0807986A2; ATE552050T1; PE20081812A1; DE102007010130B4; EP2125237B1; PL2125237T3; ZA200904612B; EP2125237A1

Description

PCT/EP2008/051403 / 2007P03823WOAU Description Method and arrangement for separating magnetic particles from a substance The invention relates to a method for magnetically separating magnetic particles from a substance, in particular for cleaning liquid mixtures, such as suspensions, sludges or the like, containing magnetic particles. In addition, the invention also relates to an associated arrangement for carrying out the method. Magnetic separators are used for separating magnetic constituents from nonmagnetic constituents in industrial processes. This can be a case of undesired impurities, for example iron impurities in aluminum scrap in the case of aluminum recycling, undesired iron constituents in wood processing or in used tire processing, or especially a targeted recovery or re-use of magnetic constituents, for example steel in concrete recycling. Such a type of separator typically consists of a facility which serves to generate strong magnetic field gradients. In this situation, both electromagnets and also permanent magnets are employed. The latter have the advantage of not requiring a separate power supply. In a magnetic field gradient, a force which is proportional to the magnetization of the body and to the gradient of the magnetic field is exerted on a magnetic body. Bodies can be magnetic either as a result of the fact that they bear their own magnetic moment or that they are magnetized by an external magnetic field, for example that of the gradient field.

PCT/EP2008/051403 / 2007PO3823WOAU 2 Based on the above prior art, the object of the invention is to set down an improved method for separating magnetic or magnetizable particles and to create an associated arrangement. In respect of the method, the object is achieved according to the invention by the measures described in claim 1. In respect of the associated arrangement, the object is achieved by the features described in claim 7. Developments of the method and of the associated arrangement are set down in the subclaims. The invention relates to a method for magnetically separating magnetic particles from a substance, wherein the substance is brought into contact with solid materials, areas of which are magnetic or magnetizable or are nonmagnetic or non magnetizable, and in said areas of the magnetizable material the magnetic constituents are continuously removed from the substance that is to be cleaned. By preference, with the method according to the invention, a cleaning of mixtures having a fluidic consistency, such as suspensions, sludges or the like, and containing magnetic particles takes place, whereby in this case the individual method steps can be carried out in a simple manner. In particular, in this situation the magnetizable areas move in the opposite direction relative to the substance to be cleaned, in other words a counterflow principle is implemented. In this situation, the magnetizable material is advantageously alternately magnetized in a first step by a first field and demagnetized in second step by a second field. In addition, it is also possible to use gradient fields with an even greater reach in order to attract further particles which are not situated in the immediate vicinity of the PCT/EP2008/051403 / 2007PO3823WOAU 3 magnetizable material. With regard to an arrangement for carrying out the method according to the invention, it is proposed to embody a continuously moving continuous belt made at least partially of areas of magnetizable material, by way of which material the substances to be cleaned or to be separated are conveyed, whereby the magnetic constituents are removed continuously from the substances in each case. With regard to the arrangement according to the invention, the following advantageous properties are in particular implemented: - The belt material in question is preferably an iron (Fe) base alloy and is in fact typically an iron/chromium (FeCr) alloy with further constituents. Stainless steel, which for example as a result of mechanical processing, typically a cold forming process, rollers for example, is present in a crystal structure which is magnetic, therefore comes into consideration as a material. With regard to stainless steel, as a general rule this is the martensitic phase which is formed or intensified by cold forming (so-called hardening martensite). Advantageously, this stainless steel belt is modified locally in such a manner that it loses its magnetizability, in other words becomes nonmagnetic, or paramagnetic. As a modification according to the invention, local heating by means of electromagnetic radiation (laser, infrared heater), by means of an inductive heater or by means of direct contact with a heating element come into consideration. Given suitable process management, a conversion of the martensitic phase into the austenitic phase may occur in this situation, whereby the martensitic phase is characterized in particular by a different crystal PCT/EP2008/051403 / 2007PO3823WOAU 4 structure, namely a cubic structure. In connection with the invention, it is essential that the conversion phase is nonmagnetic, in other words not magnetizable. - In addition, a magnetization device is provided which imparts a remanent magnetization to the conveyor belt, for example an electromagnet or a permanent magnet, over which the belt is passed. - Heat treatment of areas of the material produced a local variation in the magnetization of the material and with it a magnetization gradient which in turn causes a field gradient in an outgoing stray field. - If the material that is to be separated - as mentioned, in the form of a suspension, a thin fluid sludge or the like is placed on the belt, then the magnetic constituents of the material are attracted into this locally present field gradient and held fast to a certain degree. They therefore move together with the stray field gradient of the belt. If the application occurs in counterflow, the particles accumulate more and more until a type of saturation is reached. - If the belt loaded in this manner with magnetic particles is removed from the area of the magnetization field, the magnetic constituents remain stuck on the belt provided that the magnetic properties of the belt material have been chosen such that a remanent magnetization also persists in the field-free state (high remanence (Br) to saturation (Bs) ratio). - In the case of typical cold-rolled stainless steel sheets the latter property is created in the case of magnetization in the belt/rolling direction. - The particles separated in this manner also remain stuck after the belt material has left the liquid. - Only when the magnetic moment of the belt material is made PCT/EP2008/051403 / 2007PO3823WOAU 5 to disappear in a second magnetization step by means of demagnetization, for example in the opposing field or in a decreasing alternating field, do the gradient and thus also the forces acting on the particles also disappear. In this state it is possible to remove the magnetic particles from the belt with relative ease, for example by means of an air current or mechanically by means of brushes. - After this step, the belt is again ready to be magnetized anew, and to again pick up particles from the suspension flowing away across it. Further details and advantages of the invention emerge from the description of the figures for exemplary embodiments given below which refers to the drawing in conjunction with the claims. In the drawings: Figure 1 shows a schematic illustration of an improved magnetic separator with a revolving belt conveyor, Figure 2 shows the top view of the material used for the belt conveyor, Figure 3 shows a top view of locally heat-treated areas of the material according to Figure 2 and Figure 4 shows a cross-section of the material according to Figure 3 in order to explain the mode of action according to the invention with associated particles in the magnetic field and an associated detail section in the area of the magnetic field gradient. Devices for separating magnetic constituents from a substance, in particular substances having a fluidic consistency, can be used in many fields of technology and are referred to as magnetic separators. Of particular interest technically are separators which operate continuously and are low on PCT/EP2008/051403 / 2007P03823WOAU 6 maintenance. Described in the following is a new type of concept which allows the implementation of a type of flatbed separator, made of belt-shaped material, which has the ability to remove magnetic particles from suspensions directed over the flatbed material and to deposit them outside thereof. The advantage of this separator is its low energy requirement, the continuous process management, a low maintenance requirement and a high level of process reliability. In Figure 1, a conveyor facility 1 implemented by way of example is illustrated for use as a magnetic separator. This consists in a known manner of a continuous web belt 3 revolving over two end rollers 2 and 2'. The material comprising the belt 3 is magnetizable; this will be described further below. A magnetizer 4 and a demagnetizer 5 are fitted at appropriate positions inside the web belt 3. Magnetizer 4 and demagnetizer 5 can be implemented in a known manner, for example as a permanent magnet or an electromagnet. In particular, the magnetizer 4 can in this situation be designed such that it additionally generates a high field gradient in order to thus also move particles which are situated outside the relatively rapidly declining gradient field of the conveyor facility into the area of efficacy of the separator. Furthermore, a funnel 6 is present for loading the conveyor belt with a substance 10 containing magnetic and/or magnetizable impurities. The impurities are represented schematically as small beads and designated by way of example as 111. Furthermore, a collecting receptacle 7 is present for PCT/EP2008/051403 / 2007PO3823WOAU 7 the substance which has been freed from the impurities and is designated by 10'. Figure 2 serves to illustrate that a rolled stainless steel sheet can be used as the starting material for the magnetic separator. For example, an FeCr steel (DIN 4140) is suitable, which is martensitic after a cold rolling has typically been performed and this has ferromagnetic properties. Such a belt is designated by 21. Figure 3 illustrates the fact that a belt 21 suitable for use in the separator has untreated areas 22 which therefore according to Figure 2 are martensitic and thus ferromagnetic. As a result of local heat treatment by a device 25 locally heat-treated areas are created in the belt 21, which are austenitic and thus paramagnetic, or nonmagnetic. The device 25 is constituted for example by a laser, by an inductive heating unit, by a heater wire or similar units operated by electricity. The effect of the starting material pretreated in this way can be seen from Figure 4: In the belt 21, separate areas 22 and 23 are present, at the boundaries of which gradient fields are formed. A magnetic field is imparted by a magnet in the belt direction according to arrow 41, whereby gradient fields 42 are formed in each case at the boundaries of the areas 22 and 23. The detail section illustrated in Figure 4 serves to show that the magnetic or magnetizable particles align themselves in each case in the north-south or south-north direction and that in this situation a resulting force is produced, the magnitude of which is proportional to the field gradient. As a result of PCT/EP2008/051403 / 2007PO3823WOAU 8 the effect of the permanent magnet with its reversed polarity, north-south, the particles can thus be separated. In addition to the arrangement described, wherein the particles from a substance are placed on a conveyor belt, it is also possible to describe a converse process wherein a device which exhibits the magnetic phenomena described above is placed into a liquid containing magnetic impurities, which is located in a container. The magnetic or magnetizable particles can likewise thus be removed and separated from the substance. With regard to the method described above, it is particularly advantageous that a continuous process can be represented, wherein a simple process management is provided, where the following apply: - the magnetization and the demagnetization are two spatially and locally separate processes, by means of which a simple separation is able to take place; - only a small expenditure of energy is required, in particular if permanent magnets are used; - the belt made of stainless steel is corrosion/temperature resistant and conductive in equal measure, with the result that no static charges occur; - the belt material used can have a high magnetic moment, alloys with 1.5 Tesla saturation magnetization for example; as a result, high magnetic field gradients (> 100 T/m for example) can be formed in a small space, provided that the thickness of the suspension layered flow is typically a few mm; - the surface of the belt is smooth and flat; it can however also be perforated in order for example to specifically set up turbulence effects to provide thorough mixing.

Claims

1. A method for magnetically separating magnetic or magnetizable particles from a substance, in particular for cleaning liquid mixtures containing magnetic particles, such as suspensions, sludges or the like, comprising the following method steps: - the substance, in particular the liquid mixture, is brought into contact with solid materials, areas of which are magnetic or magnetizable or are nonmagnetic or non magnetizable, - in said areas of the magnetizable material the magnetic constituents are continuously removed from the substance that is to be cleaned.

2. The method as claimed in claim 1, characterized in that the substance containing magnetic impurities is conveyed continuously over a route which contains individual areas made of magnetizable material.

3. The method as claimed in claim 1, characterized in that a device for the continuous removal of the magnetic constituents is placed into a container with a liquid mixture containing magnetic impurities.

4. The method as claimed in one of the preceding claims, characterized in that in the area of the magnetizable material gradient fields are produced which have an effect on the magnetic constituents of the substance to be cleaned in terms of a separation.

5. Method as claimed in one of the preceding claims, characterized in that the magnetizable areas move in the PCT/EP2008/051403 / 2007P03823WOAU 10 opposite direction relative to the substance to be cleaned and a cleaning of the substance takes place using the counterflow principle.

6. Method as claimed in one of the preceding claims, characterized in that the magnetizable material is alternately magnetized in a first step by a first field and demagnetized in second step by a second field.

7. Arrangement for carrying out the method as claimed in claim 1 or one of claims 2 to 6, characterized in that a continuously movable continuous belt (3) is present, which contains at least individual areas (22, 23) made of magnetizable material, by way of which the magnetic constituents (11) are continuously removed from the substance to be cleaned (10).

8. Arrangement as claimed in claim 7, characterized in that the continuously moving belt is a revolving belt conveyor (3).

9. Arrangement as claimed in claim 7 or claim 8, characterized in that the revolving belt (3) is magnetizable in a first step at least in areas by means of a first external field and the magnetization persists at least partially even after the first external field has been deactivated.

10. Arrangement as claimed in claim 9, characterized in that the first magnetic field is a gradient field which at least partially penetrates the substance to be cleaned.

11. Arrangement as claimed in claim 7 or claim 9, characterized in that the revolving belt (3) is demagnetized in a second step by means of a second external field such that PCT/EP2008/051403 / 2007P03823WOAU 11 the magnetization approximately disappears.

12. Arrangement as claimed in one of claims 9, 10 or 11, characterized in that a static field and an alternating field are present.

13. Arrangement as claimed in one of claims 7 to 12, characterized in that means (4, 5) are present for generating magnetic fields which act alternately on a revolving belt (1 3).

14. Arrangement as claimed in claim 7 or one of the following claims, characterized in that the revolving belt (3) is made of stainless steel and exhibits a martensitic crystal structure which is formed and/or intensified by cold forming.

15. Arrangement as claimed in one of claims 9 to 14, characterized in that two magnetizable areas (22) with high remanent magnetization along a first direction are separated in each case by an area (23) which exhibits a considerably lower remanent magnetization along the first direction than the adjacent areas (22).

16. Arrangement as claimed in claim 15, characterized in that the areas (23) are paramagnetic.

17. Arrangement as claimed in claim 15, characterized in that the areas (22) exhibit a remanent magnetization which is aligned in a second direction that is approximately perpendicular to the first direction.

18. Arrangement as claimed in claim 15 or claim 17, characterized in that the first direction points in the PCT/EP2008/051403 / 2007PO3823WOAU 12 longitudinal axis of the belt (21).

19. Arrangement as claimed in one of claims 7 to 18, characterized in that the revolving belt (3) made of stainless steel has at least in part an austenitic phase which is characterized by a cubic crystal structure.

20. Arrangement as claimed in claim 19, characterized in that the austenitic phase is created by local heat treatment.

21. Arrangement as claimed in claim 20, characterized in that a magnetic gradient field is present in the areas (23) with local heat treatment.

22. Arrangement as claimed in claim 20 or claim 21, characterized in that the energy input for the local heat treatment is provided electrically, through direct heat contact, through radiation and/or inductively.